Re: [hibernate-dev] [feature request][discuss] smoother serializers integration?

I don't understand what you mean by "you put that logic in the conversion", could you elaborate? Mit freundlichen Grüßen, ------------------------------ *Christian Beikov* Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: Few more points: 1. Dto dont help at any moment - or you put that logic in the conversion and you are back to start 2. Making jaxb/jsonb easy to integrate is the goal IMO. No need to integrate with them but just provide some utility one level further than existing ones Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org&gt; a écrit : > Oops, that (3) in previous reply should have read: > 3. supporting each format creates a new "optional" library dependency > > Overall, I like Christian's approach as a potential generalized approach > to > this. Basically a combination of > > 1. a query used to provide the "view source values" > 2. some indication of how to map those "source values" to your view > model > > > And again, I think 6.0's improved dynamic-instantiation queries are a > simple, already-built-in way to achieve that for most cases. But I am > open > to discussing a way to supply that combination via API if we deem that > would be good - although then I'd also question how the current > TupleTransformer does not meet that need. > > On Thu, May 4, 2017 at 8:43 AM Steve Ebersole <steve(a)hibernate.org&gt; > wrote: > > > Were there a standard "represent something in XML-ish format" contract > > portable across a number of formats (XML, JAXB, JSON, etc) then I'd be > more > > inclined to agree with this. But as it is, supporting this would mean > > Hibernate implementing multiple such contracts, one per format. > However, > > > > 1. these formats are not our core competency > > 2. maintaining a complete set of these transformers across all the > > popular formats du-jour is a large undertaking > > 3. I am not convinced that > > > > All of these increase the technical risk. > > > > Additionally, to properly support this we'd really need the ability to > > then "map" multiple views for a given entity-graph-root. What I mean by > > that, is that such DTO approaches often need multiple "views" of a given > > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, > > CompanyDetailsGeneralDTO, etc for a Company entity. The point of this > is > > that > > > > 1. the transformers for these are specific to each DTO type and would > > be applied per-transformation > > 2. were Hibernate to "provide" this for applications > > > > IMO the use of queries to obtain views is logical. Populating each of > > those specific DTOs (CompanyListDTO, etc) in the most efficient way is > > going to require very different SQL for each DTO. This implies some > kind > > of "mapping" to be able associate each DTO with query. > > > > Given 6.0's improved dynamic-instantiation support, I even think that > is a > > great solution as well *for most cases*. > > > > So, while my objection has a "practical impact" component, I also just > > question whether Hibernate integrating with each format's "serializer" > is > > the proper solution. > > > > > > > > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < > > christian.beikov(a)gmail.com&gt; wrote: > > > >> This is exactly what I am trying to do with Blaze-Persistence Entity > >> Views, making DTOs sexy and efficient :) > >> > >> Here a quick overview of how that looks like right now: > >> > >> https://persistence.blazebit.com/documentation/entity-view/m > anual/en_US/index.html#first-entity-view-query > >> > >> One of my targets is to make it possible to do something like this > >> > >> entityManager.createQuery("FROM Order o", > OrderDTO.class).getResultList() > >> > >> and get an optimal query, as well as objects with only the necessary > >> contents. > >> > >> Maybe we can collaborate on that somehow? > >> > >> > >> Mit freundlichen Grüßen, > >> ------------------------------------------------------------ > ------------ > >> *Christian Beikov* > >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: > >> > Following up a bit on my previous email. > >> > > >> > While a core integration might be best I think, if there are too much > >> > reluctance, we can start with a dedicated hibernate-dto or whatever > >> > module or even separate project that makes life easier for these > "pass > >> > through" use cases. This could be in the form of a wrapper API of > sort > >> > and hence not affect existing Hibernate ORM APIs. > >> > > >> > Note that the ResultTransformer approach feels like it goes a long > way > >> > towards fixing the problem but as demonstrated in Vlad's article > >> > > >> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-h > ibernate-resulttransformer-to-customize-result-set-mappings/ > >> > it still requires quite a bit of code and a special DTO constructor > >> > object. That's what we need to get rid of I think. > >> > > >> > Emmanuel > >> > > >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: > >> >> I was very much in the Vlad, Steve, Christian camp until relatively > >> >> recently. One of my main concern being that replacing a proxy by > null > >> >> was really sending the wrong message. So I was against having > Hibernate > >> >> ORM facilitate such a transformation. > >> >> > >> >> I am changing my mind because I am realizing that a lot of > applications > >> >> are less complex that my perceived median. A lot of apps really just > >> >> want data to be fetched out and then passed to jackson (implicitly) > and > >> >> pushed out as a REST response in JSON or some other serialization > >> >> protocol. > >> >> > >> >> So while we could try and keep the stance that such a solution > should > >> >> remain out of scope of Hibernate ORM core, we should have a very > smooth > >> >> integration with something like MapStruct to create such bounded > DTO on > >> >> the fly. Ideally with as close to zero code as possible from the > user > >> >> point of view. > >> >> I can't really describe how that could look like because I am not > >> >> familiar enough with MapStruct but I think it should have the > following > >> >> characteristics: > >> >> > >> >> 1. do an implicit binding between the mapped object graph and a > >> detached > >> >> object graph with a 1-1 mapping of type and replacing lazy > objects > >> and > >> >> collections with null. That's the smoothest approach and the most > >> >> common use case but also the one where an inexperienced person > could > >> >> shoot at someone else's foot > >> >> 2. do a binding between the mapped object graph and a detached > version > >> of > >> >> that object graph with a 1-1 mapping of type, but declaratively > >> >> expressing the boundaries for the detached version. This > enforces a > >> >> clear thinking of the boundaries and will load lazy data in case > the > >> >> object graph loaded is missing a bit. I like the idea on > principle > >> but > >> >> I think it overlaps a lot with the fetch graph. > >> >> 3. offer a full integration between MapStruct and Hibernate ORM by > >> >> letting people express a full fledge MapStruct transformation > >> between > >> >> the managed object graph and a different target structure > >> >> > >> >> I favored MapStruct over Dozer because we know the MapStruct lead > >> quite well ;) > >> >> > >> >> Note however that the MapStruct approach requires an explicit object > >> >> copy, it feels a bit sad to have to double memory consumption. But > that > >> >> might be a good enough approach and bypassing the managed object > >> >> creation leads to questions around the Persistence Context contract > >> >> where loading an object supposedly means it will be in the PC. > >> >> Maybe a constructor like query syntax allowing to reference a > MapStruct > >> >> conversion logic might work? > >> >> > >> >> select mapStruct('order-and-items', o) from Order o left join > >> fetch o.items > >> >> > >> >> Emmanuel > >> >> > >> >> > >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: > >> >>> Hi, > >> >>> > >> >>> Although I keep on seeing this request from time to time, I still > >> think > >> >>> it's more like a Code Smell. > >> >>> Entities are useful for when you plan to modify them. Otherwise, a > DTO > >> >>> projection is much more efficient, and you don't suffer from > >> >>> LazyInitializationException. > >> >>> > >> >>> With the ResultTransformer, you can even build graphs of entities, > as > >> >>> explained in this article; > >> >>> > >> >>> > >> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-h > ibernate-resulttransformer-to-customize-result-set-mappings/ > >> >>> > >> >>> Due to how Hibernate Proxies are handled, without Bytecode > >> Enhancement, > >> >>> it's difficult to replace a Proxy with null after the Session is > >> closed. If > >> >>> we implemented this, we'd have to take into consideration both > >> Javassist > >> >>> and ByteBuddy as well as ByteCode Enhancements. > >> >>> > >> >>> all in all, the implementation effort might not justify the > benefit, > >> and > >> >>> I'm skeptical of offering a feature that does not encourage data > >> access > >> >>> Best Practices. > >> >>> > >> >>> Vlad > >> >>> > >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < > >> >>> christian.beikov(a)gmail.com&gt; wrote: > >> >>> > >> >>>> Hey Romain, > >> >>>> > >> >>>> I don't think it is a good idea to expose entities directly if you > >> >>>> really need a subset of the data. > >> >>>> Reasons for that thinking are that it gets hard to define what > needs > >> to > >> >>>> be fetched or is safe to be used for a particular use case. > Obviously > >> >>>> serialization is like a follow-up problem. > >> >>>> I see 2 possible solutions to the problem and both boil down to > the > >> use > >> >>>> of DTOs. > >> >>>> > >> >>>> 1. Use an object mapper(e.g. Dozer) that maps entity object > graphs > >> to > >> >>>> custom DTO types. > >> >>>> 2. Use specialized DTOs in queries. > >> >>>> > >> >>>> > >> >>>> Implementing 1. does not help you with lazy loading issues and 2. > >> might > >> >>>> require very intrusive changes in queries which is why I > implemented > >> >>>> Blaze-Persistence Entity Views > >> >>>> <https://github.com/beikov/blaze-persistence#entity-view-usage>;. > >> >>>> This is a library that allows you to define DTOs with mappings to > the > >> >>>> entity. In a query you can define that you want results to be > >> >>>> "materialized" as instances of the DTO type. > >> >>>> This reduces the pain induced by properly separating the > >> "presentation > >> >>>> model" from the "persistence model" and at the same time will > improve > >> >>>> the performance by utilizing the mapping information. > >> >>>> I don't want to advertise too much, just wanted to say that I had > the > >> >>>> same issues over and over which is why I started that project. > >> >>>> > >> >>>> Mit freundlichen Grüßen, > >> >>>> > >> ------------------------------------------------------------ > ------------ > >> >>>> *Christian Beikov* > >> >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: > >> >>>>> Hi guys, > >> >>>>> > >> >>>>> Short sumarry: Wonder if hibernate could get a feature to kind of > >> either > >> >>>>> unproxy or freeze the entities once leaving the managed context > to > >> avoid > >> >>>>> uncontrolled lazy loading on one side and serialization issues on > >> another > >> >>>>> side. > >> >>>>> > >> >>>>> Use case example: a common example is a REST service exposing > >> directly > >> >>>>> hibernate entities (which is more and more common with > microservice > >> >>>>> "movement"). > >> >>>>> > >> >>>>> Objective: the goal is to not need any step - or reduce them a > lot - > >> >>>>> between the hibernate interaction and a potential serialization > to > >> avoid > >> >>>>> issues with lazy loading and unexpected loading. Today it > requires > >> some > >> >>>>> custom and hibernate specific logic in the serializer which kind > of > >> >>>> breaks > >> >>>>> the transversality of the two concerns (serialization and object > >> >>>>> management/loading). > >> >>>>> > >> >>>>> > >> >>>>> Implementation options I see: > >> >>>>> > >> >>>>> 1. a callback requesting if the lazy relationship should be > fetched, > >> >>>>> something like > >> >>>>> > >> >>>>> public interface GraphVisitor { > >> >>>>> boolean shouldLoad(Object rootEntity, Property property); > >> >>>>> } > >> >>>>> > >> >>>>> 2. An utility to remove any proxy potentially throwing an > exception > >> and > >> >>>>> replacing the value by null or an empty collection, something > like > >> >>>>> > >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); > >> >>>>> > >> >>>>> 3. A switch of the proxy implementation, this is close to 2 but > >> wouldn't > >> >>>>> require a call to any utility, just a configuration in the > >> persistence > >> >>>> unit. > >> >>>>> Side note: of course all 3 options can be mixed to create a > single > >> >>>> solution > >> >>>>> like having 3 implemented based on 1 for instance. > >> >>>>> > >> >>>>> Configuration proposal: this would be activated through a > property > >> in the > >> >>>>> persistence unit (this shouldn't be only global IMHO cause > >> otherwise you > >> >>>>> can't mix 2 kind of units, like one for JSF and one for JAX-RS > to be > >> >>>>> concrete). This should also be activable as a query hint i think > - > >> but > >> >>>> more > >> >>>>> a nice to have. > >> >>>>> > >> >>>>> > >> >>>>> What this feature wouldn't be responsible for: cycles. If > >> relationships > >> >>>> are > >> >>>>> bidirectional then the unproxied entity would still "loop" if you > >> browse > >> >>>>> the object graph - this responsability would stay in the consumer > >> since > >> >>>> it > >> >>>>> doesn't depend on hibernate directly but more on a plain object > >> handling. > >> >>>>> > >> >>>>> What do you think? > >> >>>>> > >> >>>>> > >> >>>>> Romain Manni-Bucau > >> >>>>> @rmannibucau <https://twitter.com/rmannibucau> | Blog > >> >>>>> <https://blog-rmannibucau.rhcloud.com> | Old Blog > >> >>>>> <http://rmannibucau.wordpress.com> | Github <https://github.com/ > >> >>>> rmannibucau> | > >> >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau> | JavaEE > Factory > >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com> > >> >>>>> _______________________________________________ > >> >>>>> hibernate-dev mailing list > >> >>>>> hibernate-dev(a)lists.jboss.org > >> >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> >>>> _______________________________________________ > >> >>>> hibernate-dev mailing list > >> >>>> hibernate-dev(a)lists.jboss.org > >> >>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> >>>> > >> >>> _______________________________________________ > >> >>> hibernate-dev mailing list > >> >>> hibernate-dev(a)lists.jboss.org > >> >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> >> _______________________________________________ > >> >> hibernate-dev mailing list > >> >> hibernate-dev(a)lists.jboss.org > >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> > _______________________________________________ > >> > hibernate-dev mailing list > >> > hibernate-dev(a)lists.jboss.org > >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> > >> _______________________________________________ > >> hibernate-dev mailing list > >> hibernate-dev(a)lists.jboss.org > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> > > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev